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considerable amount of heat is developed in the process. The
flask is now fitted with a reflux condenser (see Fig. 40) placed
upon the water-bath and heated for 23 hours. The product
now contains in addition to ethyl hydrogen sulphate, free sul-
phuric acid and unchanged alcohol. The liquid on cooling is
poured into i litre of cold water m a large basin and well stirred.
It is neutralised by adding chalk ground into a thin paste with
water. This precipitates the free sulphuric acid as calcium sul-
phate and converts the ethyl hydrogen sulphate into the soluble

FIG. 40.
calcium salt. The mixture is heated and filtered through a
large porcelain funnel (see Fig. 36) at the filter-pump, and the
precipitate pressed well down. The clear filtrate is heated on
the water-bath and a solution of potassium carbonate (about 50
grams) is added in small quantities until the liquid is slightly
alkaline. To ensure complete precipitation a little of the clear
liquid should be tested with a solution of potassium carbonate
before proceeding.
The calcium salt is thereby converted into the soluble potas-
sium salt and calcium carbonate is precipitated. The latter is
removed by filtration, as before, and the filtrate concentrated on
the water-bath to a small volume until a drop of the liquid, re-
moved on the end of a glass rod, crystallises at once on cooling.
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